1. Field of the Invention
The present invention relates to television signal processing and, more particularly, to the generation and use of signals for television signal processing.
2. Description of the Related Art
Televisions and other types of television signal processing devices of today utilize a variety of integrated circuits, circuitry, and/or logic to provide necessary processing of television signals. Both analog and digital television signals require fairly extensive processing from receipt of the television signals to eventual display on a display device associated with the television/television signal processing device and audio output or reproduction. Such extensive processing typically correlates to extensive circuitry and/or logic for accomplishing such processing. A currently common practice in television engineering, as well as consumer electronics engineering in general, is to consolidate processing functionality. This has the advantage of reducing the space necessary for such processing circuitry/logic. Reducing circuitry/logic space is a desirable result for many reasons.
With regard to signal processing, various signals are utilized and/or generated by the processing circuitry during processing of a television signal. One such generated signal is a sandcastle signal. A sandcastle signal is a combination timing and control signal that is typically used in television signal processing, particularly analog television signal processing. A conventional sandcastle signal, as depicted in FIG. 1, reference being now made thereto, comprises a combination of pulses of different levels or voltages.
In FIG. 1, a typical sandcastle signal, generally designated 10 is shown in timing relationship with a horizontal video signal of a television signal, generally designated 20. The sandcastle signal 10 includes a first pulse or portion 12 of a first given length of time and of a first given voltage, a second pulse or portion 14 of a second given length of time and of a second given voltage, and a third pulse or portion 16 of a third given length of time and of a third given voltage. The sandcastle signal 10 is provided during the blanking interval 22 of the horizontal video signal 20. Thus, the pulses or portions 12, 14, and 16, comprise the sandcastle signal 10 and are provided during the blanking interval 22.
For comparison, the horizontal video signal 20 has a blanking interval portion 22 during which a color burst interval 26 of color burst data is provided. After the blanking interval 22, the video signal 20 has an active scan interval 24 in which video data are provided for processing.
During interval 18, the sandcastle signal is below both the blanking and keying thresholds. Therefore, the sandcastle repeats with a new period during each horizontal line of the vertical field. In a similar manner, the sandcastle signal contains a vertical blanking interval wherein the level of the sandcastle signal is held at an intermediate level during vertical blanking.
The sandcastle signal as shown is used to control horizontal and vertical retrace blanking of the luminance and chrominance output signals, disabling of the black stretch negative peak detector, sampling of the color burst signal in an automatic color control (ACC), and chroma subcarrier regenerator (color PLL (Phase Lock Loop)), and keying of the luminance back porch clamp (clamp key). These functions are shown in block form in FIG. 2.
FIG. 2 shows a block diagram depiction of the use of the sandcastle signal 10. The sandcastle signal 10 is fed to a positive (+) input of a first comparator 32 and a positive input of a second comparator 34. A negative (−) input of the comparator 32 is maintained in a high state (logic level 1) by being tied to a first battery 36a. A negative (−) input of the comparator 34 is maintained in a high state (logic level 1) by being tied to a second battery 36b. 
The comparator 32 includes an output 38 that is split into a first output 38a and a second output 38b. The first output 38a is in communication with burst-gate circuitry/logic, an ACC portion, and a chroma PLL portion of the processing circuitry. The comparator 34 includes an output 40 that is the blanking pulse to disable the luma output and black stretch negative peak detector.
A conventional manner of generating and using a sandcastle signal or pulse 10 is shown in FIG. 3, of which reference is now made, that represents by way of a block diagram a television signal processing circuitry/logic, generally designated 50. The television signal processing circuitry/logic 50 may be utilized in any type of consumer electronic device, particularly a television signal processing device and, more particularly, a television with or without an integral display. The television signal processing circuitry/logic 50 includes a sandcastle generation circuitry/logic portion (generator) 51 and a video processing circuitry/logic portion 70.
The sandcastle generator 51 is operative to receive a horizontal flyback pulse or signal and generate a horizontal blanking pulse, to receive a vertical retrace pulse or signal and generate a vertical blanking pulse, and to receive a composite video and sync pulse or signal and generate a burst-gate/clamp-key signal. Each incoming pulse or signal is received from other appropriate circuitry/logic, not shown, of the processing circuitry/logic 50.
The horizontal flyback pulse is received into signal clipper circuitry/logic 52 that processes the incoming signal appropriately and provides an output signal to timing/control circuitry/logic 54 to thereby generate a horizontal blanking pulse. The vertical retrace pulse is received in a signal clipper 56 that processes the incoming signal appropriately and provides an output signal to a vertical oscillator 58. The mixed signal from the vertical oscillator 58 provides a vertical scan signal and an output signal to timing/control circuitry/logic 60 to thereby generate a vertical blanking pulse. The composite video and sync pulse is input to a sync separator 62 that processes the composite video and sync pulse appropriately and provides an output signal to a horizontal phase-locked loop (PLL) 64. The horizontal PLL 64 also receives the output signal from the clipper 52 such that a horizontal scan signal is produced as well as an output signal that is provided to timing/control circuitry/logic 66. The timing control circuitry/logic 66 also receives the sync separator output, which, together with the horizontal PLL output signal, provides a burst-gate/clamp-key signal. The horizontal blanking pulse, the vertical blanking pulse, and the burst-gate/clamp-key signal are summed in summer circuitry/logic 68 to provide an output signal that is the sandcastle (“S.C.” in FIG. 3) signal.
The video processing circuitry/logic 70 receives the composite video and sync signal and processes the signal in luma/chroma separation filter circuitry/logic 72. The luma portion of the output signal of the luma/chroma separation filter circuitry/logic 72 is input into luma processing circuitry/logic 74 which, along with the clamp-key signal and blanking signals provides a luma processed output signal. The chroma portion of the output signal of the luma/chroma separation filter circuitry/logic 72 is input into chroma processing circuitry/logic 78 and color PLL circuitry/logic 80 which, along with the burst-gate signal, provides chroma processed output signals. Adding or mixing circuitry/logic 76 receives the luma processed output signal and the chroma processed output signals, which, along with blanking signals, provides R,G,B video output signals.
In view of the above, various unintended problems or consequences can occur within the consumer electronic device. These unintended problems may become evident only when the device is in use. One such problem that occurs in some televisions is a bright flash on the display during channel change. Typically, these televisions are operative to process analog television signals utilizing an attenuated flyback voltage to key a video clamp (video clamping circuit) for the display. The video clamp sets the black level of an analog television signal to a constant DC voltage. This is done so that the blanking bar associated with clamping is during horizontal deflection retrace. The flyback remains as the clamp pulse, after the video reappears after the channel change. The sync tip of the analog television signal is then clamped. When the standard sandcastle is switched in, the clamping moves from the sync tip to the back porch of the sync signal portion of the analog television signal. Any noticeable delay is typically due to a black stretch feature. Thus, it would be desirable to reduce and/or eliminate the flash that occurs on the television display during channel change. Of course, it would be desirable to reduce and/or eliminate other undesirable effects that may be produced during television signal processing and/or during various functions of a television signal receiver having television processing circuitry/logic, in addition to the one described in detail above.